Doors in enclosures such as houses and buildings are typically unlocked by an authorized person's insertion of a key or card into a lock on the door or entry of a numeric or alphanumeric access code into a keypad. In applications in which the authorized person is carrying one or more items, inadvertently misplaces the key or card or forgets the access code, however, entry of the person through the door becomes a challenge. Therefore, door unlocking systems and methods which facilitate automatic, wireless and hands-free unlocking of a door via a secure transmission signal as an authorized person approaches the door may be desirable for some applications.